Electronic fuel injection valve

ABSTRACT

In an electronic fuel injector used in a combustion system using gas fuel, the present invention suppresses wearing of worn portions to make control of stable supply of gas fuel possible by forming a surface reforming layer (nitrided layer etc.) having wear resistance on a surface of a structural material of worn portions of the electronic fuel injector.

FIELD OF THE INVENTION

The present invention relates to an electronic fuel injector using gasfuel, and particularly to an electronic fuel injector which improveswearing resistance of the constituting members when it is used for afuel supply system for a vehicle.

BACKGROUND OF THE INVENTION

Conventional electronic fuel injectors, in the cases of using gasolinefuel, can be roughly classified into two types, that is, a ball-typeinjector having a ball-shaped tip moving part as shown in JapanesePatent Application Laid-Open No.1-310165 and a pintle-type injectorhaving a triangular tip moving part, but the injectors of the both typesare nearly the same in the structures and the functions. That is, theelectronic fuel injector comprises a stator core; a magnet coilconcentric with the stator core; a casing formed of a magnetic material,the casing containing the stator core and the magnet coil inside; amoving part having a valve body in the tip of the moving part; a stopperfor the moving part; a valve seat opposite to the stopper, the movingpart being interposed between them; and a spring for pushing the movingpart against the valve seat by engaging with one end of the moving part.Therein, when current is conducted to the magnet coil to form a magneticcircuit and the produced magnetic force overcomes a spring force pushingthe moving part, the tip of the valve body is detached from the valveseat to open the electronic fuel injector. When the current is cut off,the valve body is moved toward the valve seat to close the electronicfuel injector.

In the fuel injector described above, the valve body in the tip of themoving part and the valve seat need to be wearing-resistant because theycollide with each other. Therefore, a material of high carbon (C) andhigh chromium (Cr) martensitic stainless steel such as JIS-SUS440C orJIS-SUS420J2 shown in the above published reference is hardened byquenching and tempering to be used for the valve body and the valveseat.

As for the conventional electronic fuel injector using gasoline fuel, inthe electronic fuel injector for a vehicle, the martensitic stainlesssteel described above can cope with the wearing resistance of theconstruction material for guaranteeing performance of the electronicfuel injector, which maintains the lifetime of the vehicle, due tolubricating and cooling power of gasoline fuel. However, in recentyears, as attention is focused on the global environmental issue,various kinds of exhaust controls are imposed on the motor vehicleindustry. As the countermeasures for the exhaust controls, electricvehicles of zero-emission are already in the market. On the other hand,a fuel system substantially cleaning exhaust gas by using gas such asnatural gas and performing precise fuel supply control using anelectronic fuel injector, which is different from the conventionalcontrol of propane gas, is being developed.

However, because such gas fuel, particularly, gas is very poor inlubricity compared to gasoline, in the conventional electronic fuelinjector for gasoline fuel there occurs a problem that worn portionssuch as the valve body and the valve seat in the components are worn.When wearing occurs, for example, in one of or both of the valve bodyand the valve seat, not only the injection characteristic of gas fuel ischanged, but also the seating performance is deteriorated particularlywhen wearing occurs in the seat portion. The deterioration of seatingperformance makes an engine difficult to start when the engine isrestarted because of fuel leakage after stopping of the engine, orcauses a problem of an explosion or a fire.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electronic fuelinjector which can perform stable control of gas fuel supply withoutwearing in the worn portions by solving the problem in the conventionaltechnology described above.

In order to attain the above object, the present invention improves wearresistance by forming a surface reforming layer having wear resistanceon a surface of a structural material of worn portions of the electronicfuel injector.

It is preferable that the surface reforming layer having wear resistanceis a nitrided layer, and it is particularly preferable that a hard filmmade of CrN, TiN, or a nitride or a carbide of a transition metal suchas BN, WC/C, or DLC (diamond-like carbon) or diamond is formed on thenitrided layer to form a composite layer. Further, the surface reforminglayer having wear resistance is an Ni—P plated layer hardened byage-hardening, or the wear resistance durability can be further obtainedby forming an Ni—P plated layer on the nitrided layer described above tomake a composite layer.

In order to improve the wear resistance of the constituting members ofthe fuel injector for gas fuel subjected to a large impact force asdescribed above, the surface reforming of the worn members is necessary,but the surface reforming is not limited to the nitrided layer or thecomposite layer using the hard film together described above. Instead ofthe nitrided layer, a carburized layer, a carbnitrided layer or asoft-notrided layer may be used. Further, it is clear that a compositelayer of the above layer and the hard film or the Ni—P plating describedabove has the effect to improve the wear resistance.

Operation of the present invention will be described below. In theelectronic fuel injector using gas for fuel, considered causes ofoccurring wear in the constituting members are as follows.

That is, for example, because the fuel is in a non-lubricant gas phase,different from gasoline, in the valve body of the moving part and thevalve seat and in the stopper and the worm portion of the moving part inthe other side of the wear, the impact load becomes approximately 25 kgfand the impact surface pressure becomes around 90 kgf/mm² in the initialstage of wearing due to a small contact surface. Therefore, mainly,impact wearing strongly acts on the structural material of theconventional fuel injector for gasoline fuel. This means that theproblem of securing of wear resistance can not be solved by using onlythe conventional structural material of the martensitic stainless steel.

Further, in regard to the sliding portions between the valve body of themoving part and the guide ring of the other side of the wear, andbetween the moving part and the bore portion of the stator core, it isfound from a duration test that an amount of wear become considerablylarge because of the non-lubricant gas atmosphere though the wearingload is small.

The present invention can provide an electronic fuel injector which cansuppress occurrence of the above-described wear and does not cause wearin the each of the worn portions even used under a gas fuel atmosphereby forming a surface reforming layer having good wear resistance atleast on one side. Preferably, on both sides of these worm portions asthe wear countermeasures of the friction wear members described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of an electronicfuel injector in accordance with the present invention.

FIG. 2 is an enlarged view showing the main portion of the electronicfuel injector shown in FIG. 1.

FIG. 3 is a graph showing the distribution of hardness along thedistance from a surface of a valve body after performing nitridingtreatment as surface reforming.

FIG. 4 is a table showing wear amounts before and after an operatingduration test by natural gas using the electronic fuel injector shown inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below,referring to the accompanied drawings. Referring to FIG. 1, the presentembodiment of the electronic fuel injector comprises a stator core 7; anmagnet coil 9 concentric with the stator core 7; a casing 8 formed of amagnetic material, the casing 8 containing the stator core 7 and themagnet coil 9 inside; a moving part 3 having a spherical valve body 1 inthe tip of the moving part 3 and a lower end moving part guide 5 fixedto a bore portion of an armature in the upper end; a stopper 4 for themoving part 3; a valve seat 2 opposite to the stopper 3, the moving part3 being interposed between them; and a spring 14 for pushing the movingpart against the valve seat 2 by engaging with one end of the movingpart 3. Therein, when current is conducted to the magnet coil 9 to forma magnetic circuit and the produced magnetic force overcomes a force ofthe spring 14 pushing the moving part 3, the valve body 1 in the tip ofthe moving part is moved upward to open the electronic fuel injector.When the current is cut off, the valve body is moved downward to closethe electronic fuel injector.

FIG. 2 is an enlarged view showing a portion of the valve body 1 and thevalve seat 2 and the moving part 3. The worm portions targeted by thepresent application are the valve body 1 and the seat portion 10 of thevalve seat 2; the stopper 4 and the collision portion 11 with the movingpart 3; the valve body 1 and the worn portion 12 with the lower endmoving part guide 6; and the upper end moving part guide 5 fixed to thearmature bore portion of the moving part 3 and the worn portion 13 ofthe stator core 7. The feature of the present invention is that thesurface of the structural material of each of the worn portions istreated with surface reforming as the wear countermeasures. FIG. 3 showsthe distribution of hardness along the distance from a surface of themoving part valve body 1 after performing plasma nitriding treatment of530° C., 3 h using DC glow discharge. The material for the moving partvalve body 1 is JIS SUS440C. It can be understood from the result thatthe hardness at the topmost surface is 1050 Hv and the total depth ofthe hardened layer is about 60 μm. The material for the valve seat 2,the moving part 3 and the stopper 4 is JIS SUS420J2, the material forthe upper moving part guide 5 is JIS SUS304, and the material for thestator core 7 is a 13Cr group magnetic stainless steel. However, thehardness distributions for these materials are almost similar to thatfor SUS 440C shown in FIG. 3.

A 500-million-cycle operating duration test of an electronic fuelinjector for gas fuel having the wear-resistant treated worn portionsand a conventional injector for gasoline using natural gas (85%butane-15% methane) as the gas was conducted. FIG. 4 shows thecomparatively measured results of the wear amounts of the valve bodies 1before and after the operating duration test. According to the results,the wear amount of the conventional fuel injector was 70˜380 μm. On theother hand, the wear amount of the electronic fuel injector for gas fuelhaving the wear-resistant treated worn portions was 3˜18 μm, and theflow rate change of natural gas was also within a target specificationof ±5%. As the result, it is clarified that the surface reformation isvery effective for the electronic fuel injector for gas fuel.

In addition to the above, a surface reforming method to further increasethe electronic fuel injector for gas fuel is that a ceramic film made ofa transition metal carbide or nitride having a thickness of several μmis further formed on the topmost surface of the plasma nitriding treatedmaterial described above. There, after plasma nitriding treatment, theplasma nitriding treated material was coated with CrN through anactivated reaction evaporation method (ARE) of the physical vapordeposition method (P.V.D) by which good adherence with the base materialcould be obtained. A film having a thickness of approximately 2 μm wasobtained under film forming conditions of reaction gas: N₂, evaporationsubstance: Cr, gas pressure: ˜0.13 Pa, electron beam power: 5 kW, 140mA, substrate applied voltage: DC −400 V, substrate temperature: ˜400°C., and coating time: 1 hour. Using an electronic fuel injector having acomposite surface reformed layer composed of a nitrided layer under thesurface of the material described above and a hard CrN film having ahardness of approximately 2000 Hv on the topmost surface, a500-million-cycle operating duration test by natural gas similar to theabove-mentioned test was conducted. The test result showed little wear.

On the other hand, there is a traditional method of improving the wearresistance, that is, Ni—P plating. In this case, precipitationage-hardening treatment was performed at 350° C. after plating in orderto increase hardness of the plating layer, and hardness of 800 Hv wasobtained. By this surface reforming treatment, wear in the sliding wormportions 12 and 13 was small, but the wear amount before and after theabove-mentioned duration test in the collision worn portion 10 and 11became 50˜85 μm. This method was inferior to the wear resistance of thenitrided layer or the CrN layer, but had an effect as wear resistantcountermeasures.

In an electronic fuel injector using gas phase fuel such as natural gas,it is possible to provide the structure which can give a stable andreliable injection characteristic by reducing wear in each of the wornportions, particularly, in the collision portions as small as possible,and is good in starting performance and safe by eliminate fuel leakageduring stopping operation of the engine.

What is claimed is:
 1. An electronic fuel injector comprised of a statorcore; a magnet coil concentric with said stator core; a casing formed ofa magnetic material, said casing containing said stator core and saidmagnet coil inside; a moving part having a valve body in a tip of themoving part; a stopper for said moving part; a valve seat opposite tosaid stopper, said moving part being interposed between said valve seatand said stopper; and a spring for pushing said moving part against saidvalve seat by engaging with one end of said moving part, said movingpart being reciprocally moved between said valve seat and said statorcore by a magnetic force produced by said magnet coil and a force ofsaid spring, wherein a surface reforming layer having wear resistance isformed on surfaces of sliding portions of said valve body in the tip ofsaid moving part and of said valve seat; surfaces of said valve body anda guide ring of said valve body; of colliding surfaces of said stopperand said moving part; and of sliding surfaces between said moving partand said stator core.
 2. An electronic fuel injector according to claim1, wherein said surface reforming layer having wear resistance is anitrided layer.
 3. An electronic fuel injector according to claim 1,wherein said surface reforming layer having wear resistance is acomposite layer of a nitrided layer and a hard film.
 4. An electronicfuel injector according to claim 1, wherein said surface reforming layerhaving wear resistance is an Ni—P plated layer.
 5. An electronic fuelinjector according to claim 1, wherein said surface reforming layerhaving wear resistance is a composite layer of a nitrided layer and anNi—P plated layer.
 6. An electronic fuel injector according to claim 1,wherein said surface reforming layer is a plated layer.
 7. An electronicfuel injector comprised of a stator core; a magnet coil concentric withsaid stator core; a casing formed of a magnetic material, said casingcontaining said stator core and said magnet coil inside; a moving parthaving a valve body in a tip of the moving part; a stopper for saidmoving part; a valve seat opposite to said stopper, said moving partbeing interposed between said valve seat and said stopper; and a springfor pushing said moving part against said valve seat by engaging withone end of said moving part, said moving part being reciprocally movedbetween said valve seat and said stator core by a magnetic forceproduced by said magnet coil and a force of said spring, wherein asurface reforming layer having wear resistance is formed on at least oneside of surface portions of sliding surfaces of said valve body in thetip of said moving part and said valve seat of worn portions; of saidvalve body and a guide ring of said valve body; of colliding surfaces ofsaid stopper and said moving part; and a of sliding portion surfacesbetween said moving part and said stator core, wherein said surfacereforming layer is selected from the group consisting of at least one ofa nitride layer, a composite layer of a nitride layer and a hard film,an Ni—P plated layer and a composite layer of a nitride layer and anNi—P plated layer.
 8. A method of using an electronic fuel injectorcomprised of a stator core; a magnet coil concentric with said statorcore; a casing formed of a magnetic material, said casing containingsaid stator core and said magnet coil inside; a moving part having avalve body in a tip of the moving part; a stopper for said moving part;a valve seat opposite to said stopper, said moving part being interposedbetween said valve seat and said stopper; and a spring for pushing saidmoving part against said valve seat by engaging with one end of saidmoving part, said moving part being reciprocally moved between saidvalve seat and said stator core by a magnetic force produced by saidmagnet coil and a force of said spring, comprising forming a surfacereforming layer having wear resistance on at least one side of surfaceportions of said valve body in the tip of said moving part and saidvalve seat of worn portions; of said valve body and a guide ring of saidvalve body; of colliding portions of said stopper and said moving part;and of sliding surfaces between said moving part and said stator core,and using the electronic fuel injector in a gas fuel supply environment.9. A method according to claim 8, further comprising selecting saidsurface reforming layer from the group consisting of at least one of anitride layer, a composite layer of a nitride layer and a hard film, anNi—P plated layer and a composite layer of a nitride layer and an Ni—Pplated layer.